ACH Calculator | Air Changes Per Hour with Examples!

The efficiency of an air purifier is determined by its ACH. ACH stands for Air Changes Per Hour. It denotes how many times the air purifier can change the air in the room in an hour. It is easy to calculate the ACH of your air purifier. All you need is a few input data, and our ACH calculator will help you determine the ACH within no time.

ACH Calculator
Enter Room Area
Air Delivery Rate in CFM (cubic feet per minute)



air changes per hour formula
Air changes per hour formula

The Input Data

  • The area of your room (in square feet) – Length x Width of your room
  • The height of the ceiling (in feet)
  • CADR of the Air Purifier (cubic feet per minute) – Information provided in the specification sheet of your air purifier

The Output Information

As soon as you enter the data, you get the output instantly.

  • ACH – Air changes in an hour
  • Time taken to purify the air in your room – in minutes

Related: Air Purifier Filters

Real-time Examples

Let us now calculate the ACH of a couple of top air purifier brands available on Amazon.

ParametersCoway Professional Air Purifier – AP-1019CMi Air Purifier 3Philips High-Efficiency Air Purifier AC2887
Area of your room (square feet)150150150
Height of the ceiling (feet)101010
CADR (cfm)178224196
Time taken to purify the air the room8.46.77.7

Points to note

  • The CADR given in the product specification sheet is generally in cubic meters per hour. However, our calculator requires CADR in cubic feet per minute. Hence, you have to refer to our CADR to CFM calculator to get the CADR in cfm.
  • If the ACH of Coway Professional Air Purifier is 7.12, it signifies that this air purifier can change the air in your room seven times in an hour. Therefore, it will take approximately eight minutes to purify the entire air in your room.
  • The ACH calculation depends on the room volume. The smaller the volume, the less time it will require to purify the air in your room. We have assumed a normal Indian bedroom with 150 square feet (15 x 10) area and a standard height of 10 feet.

Related: CADR Calculator

Tips for selecting the best air purifier for your room

  • Determine the location where you want to place your air purifier in the room. Accordingly, you can go for the right size.
  • Choose an air purifier specific to your purification needs. For example, the HEPA filter-equipped air purifiers are excellent for removing cigarette smoke and other similar pollutants.
  • Compare the CADR ratings of the different products. It shows the efficiency of the air purifier. Use our CADR to CFM calculator and the ACH calculator to understand how much time it takes to change the air in your room.
  • Air purifiers can make a lot of noise. Therefore, it is advisable to go for one that has the least decibel value.
  • Check out the air purifier power consumption to get an idea about the electricity costs you could incur.
  • Your budget is crucial. Some features like smartphone app integration are useful but not necessary. These features can push the pricing beyond your budget. They only contribute to the convenience aspect. If your budget is small, you can conveniently skip such features.
Chaithanya Vanjari
Chaithanya Vanjari
I'm Chaithanya Vanjari, the Creator and Editor-in-Chief at KitchenArena. With a decade of experience in evaluating large appliances like air conditioners, washing machines, refrigerators, and various small home devices, I possess the technical expertise needed to thoroughly review and understand the operational complexities of these appliances.


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